Muse Spark Open Is Here: Meta's Biggest Muse Model, Now Downloadable

Muse news · October 15, 2026

Meta announced Muse Spark Open, which it calls "the most capable US open-weight model to date." For the first time, a flagship Muse model is not locked inside Meta's own products: anyone can download its weights, run it on their own hardware, or use it through hosting partners — under Meta's Muse Model License.

What happened

• A very large, downloadable model. Muse Spark Open has 816 billion total parameters, with 42 billion active per token (a mixture-of-experts design), and a 1 million-token context window. It is natively multimodal: it takes in text, images, audio and video, and answers in text.
• Built for agent work, not just chat. Meta built it for coding and long-horizon agentic tasks — reading a whole codebase or a long set of documents, planning a multi-step job, using tools, checking its own work and recovering from mistakes.
• Free to download, with conditions. The weights are free on Hugging Face (as Muse-Spark-Open-816B-A42B, in BF16 and NVFP4 versions) and through Amazon SageMaker AI, Google Cloud Model Garden and Microsoft Foundry Models, under the Muse Model License: products built on it must show "Built with Muse Spark Open," and companies that sell it as a model-as-a-service with more than $20 million in gross revenue in a 12-month period need a separate agreement with Meta. No price was stated in the official Meta pages consulted for this note.
• You don't need to download it to use it. Hosted access launched through API partners including Baseten, Fireworks AI, Groq, Modal, Nebius, OpenRouter and Together AI. Meta also optimized it to run locally on two Apple M5 Ultra Mac Studios (512 GB of unified memory each) using Apple's MLX framework — a demonstration, not a normal office setup: the full weights need roughly a terabyte of memory.

What it means for your business

You will probably never download this model — and you don't need to. What matters for a small business is what it unlocks around you:

• The tools you buy get a new engine option. Developers and software vendors can now build Muse-class agents on a model they can download, fine-tune and even run privately, instead of renting every answer from a closed API. Expect business tools — support agents, document and invoice processors, coding and content helpers — to appear "powered by Muse Spark Open," and expect vendors to compete on price because the model itself is free to download.
• Privacy becomes a real selling point you can ask about. Because the model can run on a company's own servers (or through a host they choose), a vendor can credibly offer to process your customer lists, invoices or contracts without sending them to Meta's cloud. Until now, that option mostly meant weaker open models.
• Check the license before you build a product on it. The download is free, but it is not unrestricted open source: the attribution label is mandatory, and reselling it as an API at scale (over $20M in revenue) requires Meta's separate agreement. For internal use — your own agent working on your own data — the terms are much simpler.

Try this

Use Muse today to map which of your business tasks would benefit most from a private, downloadable model — so you know what to ask vendors as Spark Open-powered tools arrive:

"Act as my automation advisor. Here is my business: [what you sell, your main tools, and the data you handle — customers, invoices, contracts]. List the 5 tasks that handle my most sensitive data. For each one, tell me: what must stay private if an AI agent does it, what could safely go to a cloud AI, and one question I should ask any software vendor who says their tool is 'powered by an open AI model.' End with the 3 questions that matter most, in plain English."

Source: Meta announcement, October 15, 2026 — "Introducing Muse Spark Open, the most capable US open-weight model to date," Meta research blog: https://research.meta.ai/blog/muse-spark-open. This site is independent and not affiliated with Meta.